The present invention relates to a valve train for vehicles, and more particularly, to a device for actuating a valve using an electromagnetic force.
Generally, in an internal combustion engine, an air-fuel mixture is taken into a combustion chamber through an intake manifold, and the air-fuel mixture is burned in the combustion chamber. After burning, exhaust gas is exhausted into the atmosphere through an exhaust manifold. An intake and an exhaust valve are provided in an intake port and an exhaust port.
A system that includes the intake valve, the exhaust valve, and a device for actuating the intake valve and the exhaust valve is called a valve train. Combustion characteristics of the internal combustion engine depend on operation of the valve train, and therefore, in order to optimally control the burning process, it is important to control the operation of the valve train.
In a particular cam-type valve train, the up and down movement of the intake and exhaust valves is mechanically performed by a rocker arm that is actuated by a camshaft. Because arbitrary control of the up and down movement of each valve is not possible in a cam-type valve train, the cam-type valve train is not suitable for recent electronically controlled engine systems.
An electromechanical valve train is a system in which the open/close timing and open/close duration of the valve can be regulated by an electronic signal. Because the intake valve can regulate an amount of intake air, a throttle valve can be eliminated and pumping loss can be decreased. Further, burning can be performed in an optimal state so that exhaust gas can be decreased, and the structure of the valve train becomes simple.
FIG. 1 shows an example of the electromechanical valve train comprising a valve body 1, a first coil assembly 2 and a second coil assembly 3 that are disposed inside the valve body 1. A plate-shaped armature 4 is disposed between the first and second coil assemblies 2 and 3, and a valve 5 is connected to the armature 4. An upper spring 6 biases the armature in a downward direction, and a lower spring 7 biases the armature in an upward direction.
The valve train is arranged in such a manner that if a current is supplied to the first coil assembly 2, the armature 4 moves downward, and if a current is supplied to the second coil assembly 3, the armature 4 moves upward. Therefore, if a current is supplied to the first coil assembly 2, the valve 5 becomes open, and if a current is supplied to the second coil assembly 3, the valve 5 becomes closed. If a current is supplied to neither the first or second coil assemblies, the armature 4 is located in a equilibrium position.
However, in the electromechanical valve train, an armature plate that is made of iron is magnetized after long use. Thus, although a current is supplied to neither the first coil assembly nor the second coil assembly, an attractive force acts between the coil assemblies and the armature. If the armature is made of a permanent magnet to solve this problem, magnetism of the armature fades because of a high temperature of the combustion chamber, and the weight of the system is also increased.
In a preferred embodiment of the present invention, an electromechanical valve train comprises a housing defining a chamber, and an outer coil assembly including a first core having an first aperture formed therein and a first coil wound on the first core. The outer coil assembly is fixedly disposed in the chamber. Also included is an inner coil assembly including a second core having an second aperture formed therein and a second coil wound on the second core. The inner coil assembly is secured to the first aperture of the outer coil assembly. An armature is provided including an upper plate, a lower plate, a rod connecting the upper plate and the lower plate, and an insulator disposed between the rod and the upper plate or between the rod and the lower plate. The rod is vertically movably inserted into the second aperture of the inner coil assembly. An upper biasing member downwardly biases the armature and a lower biasing member upwardly biases the armature. In addition, a valve is connected to the lower plate of the armature.
Preferably, the first core of the outer coil assembly is made of a magnetizable material, and the second core of the inner coil assembly is made of an unmagnetizable material.
Further, it is preferable that the electromechanical valve train comprise a position adjuster for regulating a vertical position of the armature by pressurizing the upper biasing member.